1. Field of the Invention
The present invention relates to a thermal head and a printer.
2. Description of the Related Art
There has been conventionally known a thermal head for use in thermal printers that are often installed in compact information equipment terminals typified by a compact hand-held terminal, which performs printing on a thermal recording medium by selectively supplying a plurality of heating resistors with current based on printing data (see, for example, Japanese Patent Application Laid-open No. 2007-83532).
For increasing efficiency of the thermal head, there is a method involving forming a cavity portion in a substrate supporting the heating resistors. The cavity portion functions as a hollow heat-insulating layer. Accordingly, among an amount of heat generated by the heating resistors, an amount of heat transferring toward the substrate may be reduced to increase an amount of heat transferring to an opposite side of the heating resistors with respect to the substrate, to thereby increase energy efficiency required for printing.
The thermal head described in Japanese Patent Application Laid-open No. 2007-83532 has a structure in which one of an upper substrate (heat storage layer) and a support substrate, which are made of the same material such as glass, has a concave portion formed therein, and the upper substrate and the support substrate are bonded together so that the concave portion is closed to form a cavity portion inside the bonded substrates. The cavity portion may have any shape, the size of which may be larger or smaller than the size of the heating resistors as long as the size is close to that of the heating resistors when viewed from a stacking direction of the substrates.
However, if the size of the cavity portion is larger than an effective heating area of the heating resistors, there is an inconvenience that mechanical strength of the upper substrate may reduce, though heat-insulating performance between the heating resistors and the substrate may be enhanced. On the other hand, if the size of the cavity portion is smaller than the effective heating area of the heating resistors, there is an inconvenience that the heat-insulating performance may reduce, though the mechanical strength of the upper substrate may be increased.